The Fluid to Solid Transitions in Soft Materials

Harvard University, Cambridge MA

Investigators

Abstract

Soft materials are often viscoelastic, displaying characteristics of both a fluid and a solid. Often one behavior dominates, and the material is dominantly either a fluid or a solid; however, this can depend sensitively on the measurement. For example, a glassy material can be solid at frequencies typically measured, but fluid at very low or very high frequencies. Thus, the transition between fluid-like and solid-like behavior can be quite subtle, yet it can provide great insight into the behavior can be quite subtle, yet it can provide great insight into the behavior of the material. This transition between fluid-like and solid-like behavior is the overarching theme of the work proposed here. Experiments proposed include investigation of colloidal crystals, glasses and gels with confocal microscopy to look at individual particles, scattering to measure average effects, and rheology to measure bulk effects. A shear cell will be built for a confocal microscope to probe the motion of particles when subjected to shear, and laser tweezers will be used to probe local perturbations of structure. These experiments will provide insight into important fluid to solid transitions in soft materials. Many materials that are important in nature and in technology have a dual character they have both solid-like and fluid-like when squeezed from the tube or smeared on teeth, but maintains its shape and form like a solid when spread on a toothbrush. This research will investigate the nature of a wide class of materials that have this dual character, and will focus on the transformation from the fluid-like behavior to the solid-like behavior. The work will search for general features that can describe this behavior in wide classes of materials, and will investigate the structural properties of the materials that cause this behavior. The research will be highly leveraged through interactions with industry, ensuring that problems of practical and technological importance and addressed, in addition to problems of fundamental importance. In addition, the research will be coupled with educational efforts, through seminar and workshop series that enhance the researcher community for scientists in the local area, through projects that will engage undergraduate students and high school teachers for summer research, and through the design of a new course to explore creativity in scientific research.